Surf Forecasting Tuesday November 22, 2011

1. Surf ForecastingTuesday November 22, 2011 Kurt Korte Forecaster Surfline.com

2. Outline • Who Am I? • Surfline • Company Info • Tools • Marine and Atmospheric Forecasting • Tools Available • Case Studies • Hurricane Katia – Aug/Sept 2011 • Southern Hemisphere Swell – Summer 2011 • Bathymetry

3. Who Am I? • Grew up in Virginia Beach, VA • Graduate of University of Virginia with a degree in Environmental Science (2005) • Atmospheric Sciences Concentration • Graduate School at North Carolina State University (2008) • Majored in Meteorology • Thesis Work involving African Easterly Waves over central/western Africa and the eastern Atlantic

4. How Did I Get Interested in Weather and Forecasting? • Surfing • Work = Less Time to Surf • Work + School = Even Less Time To Surf • Work + School + Sports = Almost No Surf

5. How Did I Get Interested in Weather and Forecasting? • Know the weather and you can figure out when the waves will be good • Practice and school times were set, but I could make my own work schedule • So, the better I was at forecasting, the better I could make my schedule

6. How Did You Get Your Job? • Luck • Against my normal advice, occasionally, it pays not to skip school and go on a surf trip • Within a week, I was hired

7. Surfline – Early Days • “What if you could call a number any time of day and instantly get an up-to-the-minute report on surf conditions at not only one location, but dozens at once? And what if you could get an honest-to-goodness seventy-two hour forecast of expected swells? The forecast, made by weather guru Sean Collins, might be the most exciting feature of the new Surfline. The advantages of actually knowing when a swell can be expected and from what direction it will come need no explanation. Thanks to Surfline, a lot of Southern California surfers will be scoring better waves than they did in the past." SURFING MagazineSpring 1985

8. Surfline – On the Path to Today • Wavefax • Late 1980s • Surfline.com • 1995 • First Live Surf Cam • Huntington Beach in February 1996 • Followed by Pipeline cam later in 1996

9. Surfline Today • 100+ HD Cams • Thousands of Surf Spots • Daily Surf Reports • 7 and 14 day LOLA Forecasts • Written Forecasts • Point and Click Forecasts for anywhere in the world • Editorial Content

10. Surfline Today • In 2010 • Average of 142,000 unique people per day • Average of 1,750,000 per month

11. Surfline Forecast Team • Written Forecasts • Expert forecast team with over a combined 100 years of marine forecasting experience • Forecast team includes: • Two PhD's in oceanography and ocean engineering • US Navy wave modeling expert • Eight Forecasters

12. Tools on Surfline:HD Cams

13. Tools on Surfline:7 Day LOLA Forecast

14. Tools on Surfline:Nearshore Animations

15. Tools on Surfline:14 Day LOLA Forecast

16. Tools on Surfline:14 Day LOLA Forecast

17. Tools on Surfline:LOLA Buoys

18. Quick Buoy Case StudySurface Analysis

19. LOLA Buoys NDBC

20. Comparison of Buoy ReadingsNDBC vs Surfline’s LOLA

21. Comparison of Buoy ReadingsNDBC vs Surfline’s LOLA

22. Comparison of Buoy ReadingsNDBC vs Surfline’s LOLA

23. Buoys • Great tool for observations but also verification • Unfortunately, you need buoys in the right places for them to be useful • A buoy that is only 25 miles or so off the coast, though great for observations, gives us little in the way of forecast lead time

24. Marine Forecasting • Now that we have an idea of the some of the tools on Surfline, let’s look at some other tools and information that is out there that can help us make a solid forecast

25. Marine and Atmospheric Forecasting:Models • Atmospheric Models • Global • NWS/Global Forecast System (GFS) • Navy Operational Global Prediction System (NOGAPS) • United Kingdom Met Office model (UKMET) • European Center for Medium-range Weather Forecasting (ECMWF) Model • Tropical Cyclones • NWS/Geophysical Fluid Dynamics Laboratory (GFDL) model • NWS/Hurricane Weather Research and Forecasting Model (HWRF)

26. Marine and Atmospheric Forecasting:Models • NOAA WAVEWATCH III • Driven by winds from the operational GFS • Winds are converted to 10m height assuming neutral stability (*assumption*) • 1.25° x 1° resolution • 4 model cycles (00z, 06z, 12z, 18z) • With a 6h hindcast to assure continuity of swell • No wave data assimilation • Based on shallow water physics without mean currents • Sea Surface Temperatures as needed in the stability correction for wave growth are obtained taken from the Global Data Assimilation Scheme

27. Marine and Atmospheric Forecasting:Models • Western North Atlantic (WNA) regional model • Obtains hourly boundary data from the global model • 0°-50°N 98°-30°W Domain with 0.25° resolution • North Atlantic Hurricane (NAH) regional model • Obtains hourly boundary data from the global model • 0°-50°N 98°-30°W Domain with 0.25° resolution • Wind fields are blended with GFDL hurricane winds when possible

28. LOLA Initializes with adjusted wind speeds from various global models Data Assimilation Jason Satellite Buoy Data Ship Data Takes into account how swells are distorted by offshore islands and the continental shelf Nearshore Modeling Finer resolution in the shallow water environment Wavewatch III Initializes with winds from the operational GFS No Data Assimilation Courser resolution limits ability to properly propagate wave energy Course blocking put into model Minimum depth in model is 25m LOLA vs Wavewatch III So, by running our own models we have tremendous flexibility and resolution to accurately calculate surf heights for any point on Earth

29. Remote Sensing • Jason Satellite • Continuous ocean surface topography measurements that began in 1992 with the TOPEX/Poseidon satellite and continued with the Jason-1 satellite in 2001 • Monitor the variation of the global mean sea level and its relation to global climate change • Provide estimates of significant wave height and wind speeds over the ocean

30. Remote Sensing • QuikSCAT • Launched 1999 • Provided near-real-time ocean- surface wind speed and direction data over 90 percent of the global ocean every day • Roughly 1800 km wide swath • Died November 23, 2009

31. Remote Sensing • ASCAT • 2007-Present • 500 km wide swaths • Measures up to ~95kts • Currently Operational • Less susceptible to rain flags than QuikSCAT • Significant low bias at stronger wind speeds (over ~50kts) • Can be 10-15kts lower than QuikSCAT obs at high wind speeds

32. ASCAT vs QuikSCATHurricane Hanna 2008 What are the major differences between the two?

33. Moving On… • Now that we have an idea of the tools that are out there, let’s review some basic marine forecasting principles and go from there

34. Key Components to Wave Growth? • Wind Speed • Wind Duration • How long the wind affects a given distance • Fetch or Fetch Length • The distance over which the wind blows from a constant direction and at a constant speed

35. Since we already have a good handle on wind speed and duration, let’s take a look at identifying and locating fetches

36. Determining Fetch Boundaries • Need to find where the wind blows from a constant direction and at a constant speed • Understanding how the fetch region is changing or how many different fetch regions exist can help the forecaster confirm that the numerical wave models are correct in their analysis and forecasts

37. Determining Fetch Boundaries • When evaluating fetch, a forecaster only needs to be concerned with the fetches that will propagate waves into the forecast area • There are no set guidelines to determine the fetch boundary since changes in wind speed and direction can be fairly subtle over open water

38. Determining Fetch Boundaries

39. Determining Fetch Boundaries • Of course, the previous examples are a snapshot…in real time wind speed and direction are constantly changing • This can become very complicated, especially with a compact, intense area of low pressure, such as a tropical cyclone

40. Tropical Cyclones • Obviously can be very strong with wind speeds in excess of 100kts over a small area • Small but intense fetches develop due to the wind patterns around low pressure • This leads to chaotic seas and a difficult forecast • Models do a poor job • Lack of model resolution of strongest winds • Lack of dependable observations • Who wants to be on a ship in the middle of a hurricane? • Incorrect intensity initializations and forecasts • If the initial conditions are incorrect, this can lead to extensive errors through the forecast period • We will discuss this more later when we look at Hurricane Katia

41. Tropical Cyclones • From an operational standpoint, it is advantageous to divide the surface wind field of an intense tropical cyclone into two parts • Broad region of the cyclone that contains tropical storm force winds capable of generating swell that can affect a large expanse of ocean and coastline • Second part is the wind field in and just outside of the eyewall. This more narrow area generates extreme seas and swell that propagate in a focused great-circle path.

42. Dynamic Fetch • When storm systems move, waves in the right quadrant, or right of track, may grow larger than expected because the waves are moving in the same direction as the advancing fetch • Complicated because of the non-linear relationship between wind speed, duration, fetch and the storm speed, of the wave-generating cyclone

43. What’s It Take To Develop a Major Swell? • USS Kitty Hawk in the Western Pacific • Kitty Hawk is more than 1,000 feet long and the deck is about 40 feet above the ocean surface • Winds: 40-50 knots. Seas: 35-45 feet.

44. What Kind of Surf Would This Storm Send Us? • We expect significant swell decay within the first 1000 miles and a slower rate of decay after 2000 miles from the storm fetch • For Most Surf Spots: • Estimated Surf 1000 miles away: 15-30 foot+ faces • Estimated Surf 2000 miles away: 12-20 foot faces • Estimated Surf 4000 miles away: 8-12 foot faces • Estimated Surf 5000 miles away: 6-10 foot faces

45. Creating A Forecast • Whenever doing a forecast, the first question you should ask yourself is: What is happening right now?

46. How To Make A Forecast • Look Outside! • If it is a short term forecast you can learn a lot about what is going on outside • Is it raining? Cloudy? Snowing? Hail? Lightning? • Take a look at regional observations • Look ‘Upstream’

47. How to Make a Forecast • Other types of observational data • Remote Sensing • Radar • Satellite Derived Winds • Altimetry • Satellite Images • Upper Air Data Upstream

48. How To Make A Forecast

49. Creating A Forecast • As we have seen, observations are crucial • Unfortunately, the observational network over the ocean is scarce, at best • What tools do we have available? • Satellites • Buoy Data • Ship Observations • Nearshore Observations (ie checking the surf)

50. Case Study – Hurricane Katia